Four Vaccines Associated with Decreased Dementia Risk
The influenza, herpes zoster (shingles), tetanus-diphtheria-pertussis (Tdap), and pneumococcal vaccines have all been linked to a decreased risk of developing dementia in older adults.
Evidence for Each Vaccine
1. Influenza Vaccine
Influenza vaccination has shown significant association with reduced dementia risk. A 2023 meta-analysis of cohort studies found that influenza vaccination could reduce dementia risk by 31% (RR = 0.69,95% CI: 0.57-0.83) 1. This protective effect was observed during follow-up periods ranging from 4 to 13 years.
The American Heart Association/American Stroke Association guidelines note that influenza vaccination is associated with lower all-cause mortality in older adults, including a 65% reduction in stroke, which may indirectly contribute to reduced dementia risk 2.
2. Herpes Zoster (Shingles) Vaccine
The recombinant shingles vaccine (Shingrix) has demonstrated a strong association with decreased dementia risk. A 2024 study found that the recombinant vaccine was associated with a 17% increase in diagnosis-free time, translating to 164 additional days lived without a dementia diagnosis 3.
A population-based cohort study using UK Clinical Practice Research Datalink found that zoster vaccination was associated with a 22% lower risk of dementia diagnosis (adjusted HR 0.78,95% CI: 0.77-0.79) 4.
3. Tetanus-Diphtheria-Pertussis (Tdap) Vaccine
Tdap vaccination has been linked to significantly reduced dementia risk. A 2021 study found that patients who received Tdap vaccination had a 42% lower risk for dementia compared to unvaccinated individuals (HR = 0.58; 95% CI: 0.54-0.63) 5. This finding was consistent across different cohorts with varying clinical and sociodemographic characteristics.
4. Pneumococcal Vaccine
Pneumococcal vaccination has been associated with reduced dementia risk, though the evidence is included in studies examining multiple vaccines. The Advisory Committee on Immunization Practices recommends pneumococcal vaccines for adults with risk factors such as chronic heart, lung, liver disease, diabetes, or alcoholism 6.
Synergistic Effects of Multiple Vaccinations
Research suggests that receiving multiple types of vaccinations may provide greater protection against dementia than single vaccinations. A 2022 study found that patients who received both herpes zoster and Tdap vaccinations had a significantly lower dementia risk compared to those who received only one vaccine type or no vaccines (HR = 0.50; 95% CI: 0.43-0.59) 7.
Potential Mechanisms
The protective effect of these vaccines against dementia may be due to:
- Reduction in systemic inflammation
- Prevention of infections that could trigger neuroinflammatory processes
- Non-specific immune system modulation that may protect against neurodegenerative changes
- Reduction in vascular complications that contribute to dementia risk
Clinical Implications
These findings suggest that maintaining recommended adult vaccination schedules may have benefits beyond preventing the targeted infectious diseases. Current guidelines recommend:
- Annual influenza vaccination for all adults 6
- Herpes zoster vaccine (Shingrix) for adults ≥50 years 6
- Tdap boosters every 10 years for all adults 6
- Pneumococcal vaccines for adults with risk factors 6
Conclusion
While more research is needed to fully understand the mechanisms behind these associations, the evidence suggests that influenza, herpes zoster, Tdap, and pneumococcal vaccinations may all contribute to reduced dementia risk. This provides additional rationale for ensuring adults receive recommended vaccinations beyond the primary prevention of infectious diseases.